In surgical operations, such as an endoscopic operation, an isotonic solution has conventionally been perfused into an abdominal cavity to secure a space in which an endoscope and surgical instruments can be placed within the abdominal cavity (refer to Patent Document 1, for example). In a case where the isotonic solution is perfused in the abdominal cavity as described above, occurrence of bleeding or the presence of a floating tissue piece during surgery performed in a body cavity will cause the isotonic solution to become cloudy, which, in turn, makes an endoscopic field blurred. For this reason, a mixture liquid of the isotonic solution and a foreign substance, such as blood, is discharged out of the body to remove the foreign substance through filtering means, and the filtered isotonic solution is reinfused (returned) into the abdominal cavity.
As the filtering means, for example, hollow fiber membrane modules are used. In such a hollow fiber membrane module, a bundle of hollow fiber membranes is housed within a cylindrically shaped column. The mixture liquid of the isotonic solution and foreign substance is made to flow from end openings of the hollow fiber membranes into the hollow fiber membranes. The mixture liquid is filtered through the hollow fiber membranes to isolate the foreign substance from the isotonic solution. The filtered isotonic solution is feed into the body cavity again.